Direct column coupling

Direct column coupling is a very effective measure for process simplification as it has the potential to reduce the investment as well as the operating costs. This technique for process simplification should be used whenever possible. The only prerequisite is the existence of gas and hquid streams with approximately same concentration in different parts of the process. Such situations can often be detected by careful process design. 

Fig. 11.2-8 Flow sheet of the a-path left) and the c-path (right) with side columns. The energy demand of both processes is the same. In the shaded concentration range this process is superior to the a/c-path with direct column coupling...

Huang M.Q. et al., 2006. Increased productivity in quantitative bioanalysis using a monohth column coupled with high-flow direct-injection hquid chromatography/tandem mass spectrometry. Rapid Commun Mass Spectrom 20 1709. 

Zeng H., Deng Y., and Wu J., 2003a. Fast analysis using monolithic columns coupled with high-flow online extraction and electrospray mass spectrometric detection for the direct and simultaneous quantitation of multiple components in plasma. J Chromatogr B 788 331. 

Aldstadt et al. described the determination of U in groundwater using a FI system with a TRU-Resin column coupled on-line to an ICP-MS. The system used three 2-position valves and a flow-reversal scheme to load the sample in one direction and elute in the reverse direction. The system provided an enrichment factor on the order of 30-fold compared to direct groundwater analysis. Separate elution of Pu and Th in a group prior to eluting U was also discussed. 

Two approaches to the venting of the solvent prior to the detector have been presented in detail [137], Packed GC columns coupled to capillary columns have been used for the total transfer of effluent from the LC [138]. The current status of LC-GC has been reviewed [139]. The use and performance of the ELCD, NPD, and FPD GC detectors in liquid chromatography has also been reviewed [140]. Even though the majority of applications are not directly related to the analysis of pharmaceuticals, they may nevertheless be useful [141-146]. 

Zeng, H. Deng, Y Wu, J.-T. Past Analysis Using Monolithic Columns Coupled with High-flow On-line Extraction and Electrospray Mass Spectrometric Detection for the Direct and Simultaneous Quantitation of Multiple Components in Plasma, J. Chromatogr, B 788,331-337 (2003). 

In HPLC, the direct serial coupling of achiral and chiral columns for the simultaneous achiral/chiral separation of a range of components in a complex mixture was not feasible due to either the increased backpressure or the different mobile-phase requirement. However, this concept is not restricted for SFC because the supercritical fluid not only has a significantly lower viscosity than a liquid but is also an effective eluent for both chiral and achiral stationary phases [52], As an example, an SFC-MS approach using the coupled achiral/chiral column combination was reported to significantly enhance the separation efficiency for the reaction mixtures of cinna-monitrile and hydrocinnamonitrile intermediates to determine the diastereometric/ enantiometric composition of the final product in one step [52], Characterization of... 

For the first time, Heins et al. (1966) analyzed the head-space vapors by their direct injection on a GC capillary column coupled to a mass spectrometer, eliminating by this procedure the danger of artifact formation occasionally due to concentration procedures. Unfortunately a number of technical imperfections had to be worked on, particularly the blocking of the capillary by dry ice during the injection. 

Oliveira and Cass described a method for the analysis of cephalosporin antibiotics in bovine milk using RAM columns for on-line sample clean-up. The system was composed of a RAM bovine serum albumin (BSA) phenyl column coupled to a C18 analytical column. Milk samples were directly injected after addition of 0.8 mM solution of tetrabutylammonium phosphate. The standard curve was linear over the range 0.100-2.50 tig/ml for five cephalosporin antibiotics (cefoperazone, cephacetril, cephalexin, cephapirin, and ceftiofur). The limits of quantification and detection reported were 0.100 and 0.050 ttg/ml, respectively. The method showed high intermediate precision [coefficient of variation percent (CV%) 2.37-2.63] and recovery (CV% 90.7-94.3) with adequate sensitivity for drug monitoring in bovine milk samples. 

Several strategies have been employed in MDLC separations for proteomic studies. These strategies include discontinuous offline or online MDLC using fraction collection, direct online coupling of two dimensions, and MDLC using column switching. A major advantage of MDLC for proteomic studies... 

---